(on underfloor heating up to residual moisture ≤ 5 CM-%) when used as a primer before applying floor leveling compounds Solvent-free according to TRGS 610, no pollution of the environment and the processor by solvent vapors, no risk of fire or explosion. As a primer for PCI seals and PCI coatings on cementitious substrates, mastic asphalt screeds, ceramic coverings, synthetic resin coatings and wooden substrates. As a primer for indoor floors before applying floor leveling/filling compounds, also when subsequently gluing parquet floors - Substrates with adhesive residues from dispersion, reactive resin, water-soluble (e.g. sulfite blue adhesives) and bitumen-containing covering adhesives. Mono[(C12-14-alkyloxy)methyl]derivatives, formaldehydes, oligomeric reaction products with 1-.